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Report on Poas (Costa Rica) — 6 April-12 April 2022


Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 6 April-12 April 2022
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2022. Report on Poas (Costa Rica) (Sennert, S, ed.). Weekly Volcanic Activity Report, 6 April-12 April 2022. Smithsonian Institution and US Geological Survey.

Weekly Report (6 April-12 April 2022)


Costa Rica

10.2°N, 84.233°W; summit elev. 2697 m

All times are local (unless otherwise noted)

OVSICORI-UNA reported that on 6 April at 0240 a phreatic explosion from a vent called “Orange Fumarola” located in a fumarolic field along the inner N crater wall at Poás generated a plume that rose 500 m above the crater rim. Activity lasted for three minutes. The event caused a small landslide that modified the vent. Some of the material from the landslide was deposited in a narrow strip about 100 m into the Boca A lake. Stirred sediment was visibly moving in convection cells, turning the lake water from green to a uniform milky gray color as the sediment mixed into the water. Subaerial fumarolic vents at the E and S parts of the lake more vigorously emitted gasses following the event and remained at that level at least through 12 April. Convection in the lake also continued. OVSICORI-UNA noted that satellite data acquired the day before the explosion showed a total of 500 tons of sulfur dioxide released from both Poás and Turrialba.

Geological Summary. The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)